Gas turbine engines, such as those used to provide thrust to an aircraft, are internal combustion engines that use air as the working fluid. In general, gas turbine engines may include, among other features, a fan section and a core engine located downstream of the fan section. In operation, air may be drawn into the engine and accelerated by the fan section, and a fraction of the indrawn air may be routed through a primary flow path defined by the core engine. In an upstream to downstream order, the core engine may include: 1) a compressor section which may include a low pressure compressor (LPC) and a high pressure compressor (HPC), 2) one or more combustors, 3) a turbine section, and 4) an exhaust nozzle. In the primary flow path, the air may first be compressed/pressurized in the compressor section and it may then be combusted with fuel in the combustor(s) to generate hot combustion gases. The hot combustion gases may then expand through the turbine section, where energy may be extracted to drive the rotation of the turbine section, the compressor section, and the fan section, as all may be mounted on one or more common shafts. The gases may then be exhausted through the exhaust nozzle to provide forward thrust to an associated aircraft, or to provide power if used in other applications.
The compressor section and the turbine section may include alternating stages of stator assemblies with stationary airfoils (vanes) and rotor assemblies with rotating airfoils (blades). In rotor assemblies, the blades may be attached to a rotating disk or hub. In stator assemblies, the vanes may extend between two stationary (non-rotating) shrouds, including an inner diameter (ID) shroud and an outer diameter (OD) shroud located radially outward of the ID shroud with respect to an engine central axis.
Depending on the local temperatures and the materials making up the core engine components, the core engine components may undergo subtle thermal expansion or contraction. Unlike other regions of the core engine which are exposed to hot compressed and/or combusted gases, the inlet stator assembly of the LPC is exposed to lower temperature air that has not yet undergone compression or combustion. Due to the relatively low gas temperatures in the local flow path, the inner diameter (ID) shroud of the inlet stator assembly may be formed from lightweight materials such as aluminum which has a higher coefficient of thermal expansion (CTE) than higher strength metals such as titanium and nickel based alloys used for other engine components. Therefore, the ID shroud of the LPC inlet stator assembly may expand and contract more readily in response to temperature fluctuations than titanium- or nickel alloy-based components of the gas turbine engine.
At certain flight points, the ID shroud of the LPC inlet stator assembly may be driven to radial contraction due to exposure to a relatively cold gas path. However, the ID shroud may be mated to an upstream titanium-based bearing support and fan intermediate case which may be driven to radial expansion due to exposure to hot engine oil. The conflicting expansion/contraction tendencies and expansion/contraction rates may lead to a thermal fight between the fan intermediate case/bearing support and the ID shroud of the LPC inlet stator assembly. This occurrence may ultimately lead to stresses and/or low cycle fatigue issues in the ID shroud of the LPC inlet stator assembly.
Thus, there is a need for engine designs which mitigate or eliminate stresses caused by thermal growth mismatches between fan intermediate cases/bearing supports and ID shrouds of LPC shrouds of LPC inlet stator assemblies. U.S. Pat. No. 7,025,563 discloses the use of an outer shroud seal to accommodate thermal growth mismatches between an aluminum-based outer shroud of a LPC exit stator assembly and other titanium-based stator assembly components. While effective, the design does not address thermal fight issues between fan intermediate cases and ID shrouds of LPC inlet stator assemblies. The present disclosure addresses this problem.